The invention concerns a process and an appliance for checking the quality of formings executed by a machine for forming tube ends.
Machines for forming tube ends conventionally comprise means for holding a tube which are suitable for positioning it so that it extends on a longitudinal axis (x), called the forming axis, at least one tool for forming an end of the said tube, and means of translationally displacing each tool which are capable of displacing it on the axis (x), between an advanced forming position suitable for enabling the end of the tube to be formed and a retracted position suitable for allowing the unloading of the formed tube and the loading of a new tube.
The quality of the formings executed by such forming machines depends on a multitude of parameters, such as, in particular: the longitudinal positioning of the end of the tube, the wear of the forming tool, the thickness of the tube, the risk of rupturing of the tube, the hardness of the tube material, the possible absence of a component to be inserted on the end of the tube, the diameter of the tube, the advanced position of the tool, any slippage of the tubes in relation to the means of holding the latter, etc.
The fact of not taking account of any one of these parameters, or of experiencing a variation or absence of one of these parameters, results in a forming being obtained which is likely not to conform to the required conditions.
At the present time, the only solution which is aimed at rendering possible verification of the conformity of executed formings consists in sampling, by checking some tubes from each series of formed tubes. However, in consideration of the multiple parameters, mentioned above, which can alter the quality of the executed formings, it proves that these simple, limited checks do not enable the quality and conformity of all the tubes of a given series to be guaranteed. In practice, when use is made of the formed tubes, such checking by means of sampling proves to result in both a not insignificant wastage and numerous malfunctions resulting from a forming fault of the tubes formed thus.
The present invention seeks to overcome these disadvantages, its principal object being to provide a process for checking the quality of formings executed by a forming machine by which the conformity of formings to the required standards and conditions can be guaranteed.
To this end, the invention relates to a checking process according to which the forming machine is equipped with a force transducer which is capable of measuring the reactive axial force exerted by the tube on the tool in a forming pass and, for each forming:
in a preliminary learning phase, the maximum reactive axial force exerted by the tube on the tool is measured, the quality of the executed forming is verified in conventional manner and the value of the maximum reactive axial force obtained in a forming of a quality meeting the required conditions is recorded,
then, in each forming pass, the maximum reactive axial force exerted by the tube on the tool is measured, the value of the said maximum force is compared with the recorded reference value and the forming is validated if the measured maximum axial force corresponds to the reference force with a predetermined tolerance.
The origin of the invention was to ascertain that any variation of any one of the parameters capable of affecting the quality of formings executed by a forming machine systematically results in a variation of the maximum reactive axial force exerted by the tube on the tool. On the basis of this finding, which is not self-evident, the proposed solution according to the invention therefore consists in evaluating and recording, in a preliminary learning phase, the maximum reactive axial force exerted by the tube on the tool, then, in each forming pass, validating the executed forming if the maximum axial force measured in this forming corresponds to that recorded.
Such a process thus enables defective tubes to be detected when the tubes are formed, thereby making it possible to obtain and provide series of tubes of a quality which conforms to the required conditions.
For the purpose of perfecting the quality of the checks on the executed formings, the forming machine is also equipped, advantageously, with a linear displacement transducer which is capable of measuring the position of the tool and, for each forming pass:
in the preliminary learning phase, the reactive axial force exerted by the tube on the tool in relation to the displacement of the said tool is measured, the quality of the executed forming is verified in conventional manner, and the development curve of the reactive axial force in relation to the displacement of the tool, obtained in a forming of a quality meeting the required conditions, is recorded,
then, in each forming pass, a development curve of the reactive axial force in relation to the displacement of the tool is compiled, this curve is compared with the recorded reference curve, and the forming is validated if the two curves are identical with predetermined tolerances.
This advantageous approach results from the fact that it has been ascertained, not being self-evident, that not only the maximum reactive axial force exerted by the tube on the tool was characteristic of the executed forming, but also the development curve of the force exerted in relation to the positioning of the tool. Such an development curve of the exerted force constitutes a recordable signature which is capable of rendering possible better verification of the quality of the executed formings.
Again for the purpose of perfecting the quality of the checks on the executed formings, a checking station is advantageously added to the forming machine, comprising at least one computer-assisted camera which is suitable for viewing the formed ends of the tubes, then, for each forming:
in a preliminary learning phase, the executed forming is viewed, the quality of the latter is verified in conventional manner, and the specific data inherent to the said forming is recorded, such as physical data, surface condition and design data, as well as to any operations preceding and/or succeeding the said forming, corresponding to a forming of a quality meeting the required conditions,
then, in each forming pass, the executed forming is viewed, the data of the said forming is compared with the recorded reference data, and the forming is validated if the said data correspond with predetermined tolerances.
The addition of this viewing of the executed formings to the performance of the measures and comparisons described above is a means of guaranteeing the quality of the checks performed and, consequently, the total effectiveness of the checking process according to the invention. In addition, it not only permits validation of the executed forming, but also of any operations performed before and/or after the said forming, such as the fitting of a seal, nut, component, rolling operation, brushing operation, etc.
The following are non-exhaustive examples of defects which can be detected in this way:
cracks in the tubes
poor pickling of the tubes
defects resulting from the presence of slivers adhering to the forming tools
components mounted the wrong way round
defects resulting from scratches on the forming tools.
Furthermore, for the purpose of such viewing, advantageous use is made of at least one xe2x80x9cCCDxe2x80x9d type electronic scanning camera.
The invention includes a machine for forming tube ends, comprising means for holding a tube which are suitable for positioning it so that it extends on a longitudinal axis (x), at least one tool for forming an end of the said tube, and means of translationally displacing each tool which are capable of displacing it on the axis (x), between an advanced forming position suitable for enabling the end of the tube to be formed and a retracted position suitable for allowing the unloading of the formed tube and the loading of a new tube.
According to the invention, this forming machine comprises:
an axial force transducer capable of measuring the reactive axial force exerted by the tube on the tool,
a programmable unit, connected to the force transducer and comprising means of recording the maximum reactive axial force obtained for given forming passes, and programmed to compare, for each forming pass, the maximum axial force obtained with the corresponding recorded reference force, and to provide information concerning the validation or otherwise of the forming according to the result of this comparison.
In addition, this forming machine advantageously comprises a linear displacement transducer capable of measuring the position of the tool, the programmable unit being connected to the said linear displacement transducer and to the force transducer and:
comprising means of recording development curves of the reactive axial forces in relation to the displacement of the tool, obtained for given forming passes,
being programmed to compare, for each forming pass, the obtained development curve of the reactive axial force with the corresponding recorded reference development curve, and to provide information concerning the validation or otherwise of the forming according to the result of this comparison.
Furthermore, this forming machine is advantageously connected to a checking station comprising at least one camera which is positioned so as to view the end of each tube after forming of the latter, each of the said cameras being connected to a programmable unit equipped with means of recording specific data inherent to the different executed formings, such as physical data, surface condition and design data, as well as to any operations preceding and/or succeeding the forming, and programmed to compare, in each forming operation, the data obtained with the corresponding recorded reference data, and to provide information concerning the validation or otherwise of the forming according to the results of these comparisons.
Furthermore, each camera can be advantageously disposed so that it views the formed tube end axially.
It can also be advantageously disposed so that it views the formed tube end longitudinally.
In addition each camera is advantageously a xe2x80x9cCCDxe2x80x9d type electronic scanning camera.